Retardation coil for composite sets



' June 10, 1930. E. 1.. SCHWARTZ Er AL RETARDATION COIL FOR COMPOSITESETS Filed Nov. 1, 1927 aw M5 W y, AH t 0 N m Wm n E 2 4 n DUEL n 1 A wM. Y M 5 Patented June 10, 1930 UNITED STATES PATENT OFFICE ERNEST L.SCHWARTZ, OF EAST ORANGE, NEW JERSEY, AND ALBERT J. WILLIAMS, JR.,

OF MEDIA, PENNSYLVANIA, ASSIGNORS TO BELL TELEPHONE LABORATORIES, IN-CORPORATED, OF NEW YORK, N. Y., A CORIPORATION OF NEW YORK RETARDATIONCOIL FOR COMPOSITE SETS Application filed November 1, 1927. Serial No.230,219.

This invention relates to composite sets used in conjunction withsuperposing telegraph channels and telephone channels upon the same linecircuits and especially to retardation coils utilized in connection withcomposite sets.

Some means must be provided in a composite set for directing telephoneand telegraph signals into their respective channels. Such means maycomprise a condenserin the telephone circuit for separating thetelegraph signals from the telephone .lines while an impedance which ishigh to voice frequencies and which readily passes the telegraph signalsmay be provided in the telegraph circuits to prevent the voice currentsfrom reaching the telegraph instrument. In the prior art the impedancethus provided is known as a retardation coil. Where composite sets areused in connection with phantom circuits and where a telegraphinstrument is associated with each side of a telephone line, it isessential, in order to prevent cross-talk to maintain the impedance ofboth sides of the line in exact balance. Furthermore, there should be nocoupling between the coils associated with each telegraph instrumentsince this would produce cross-fire, or operation of one telegraphsounder when a message is being received by the other.

One object of this invention is to maintain theimpedance of both sidesof the telephone line forming one branch of the phantomcircuit balanced,when telegraph instruments are associated with both sides of the linethrough composite sets.

A related object of the invention is to eliminate cross-fire between twotelegraph instruments which are connected to a telegraph line throughthe same composite set.

Another object is to eliminate the coupling between coils having acommon core and still maintain the ratio which the .impedances of thecoils bear to each other constant for different frequency and current.

A feature-of the invention resides in a retardation coil systemcomprising two coils which have the same flux paths and in which thewindings of the coils are arranged so that a voltage individual toeither of the coils will not induce any voltage in its associated coil,but wherein an inductance change in one will create a correspondingchange in the inductance of the other.

A better understanding of the invention may be had from the followingdescription in conjunction with the accompanying drawing, in which:

Fig. 1 shows one half of a phantom circuit having telegraph soundersassociated therewith which are connected to a telephone circuit by themeans of the invention.

Fig. 2 shows the invention used to bypass telegraph signals around avoice frequency repeater.

In Fig. l a composite set C is shown associating two telegraphinstruments 1 and 2 which may either be senders or receivers withdifferent sides of telephone lines 3 and 4 forming one branch of aphantom circuit. In order not to complicate the drawing a completephantom circuit is not shown since circuits of this type are well knownin the art. Such a circuit is shown in the U. S. patent to J. Mills, No.1,351,863, granted September 7, 1920, if it be considered that therepeater therein shown be replaced by telephone terminal sets. The otherside of the phantom circuit may be identical with that shown. The lead 5from the phantom repeating coil (not shown) is connected at the midpoint6 of one winding of the repeating coil 7. This connection must always beat the electrical midpoint of the line comprising wires 3 and 4 toprevent cross-talk.

The telegraph instruments 1 and 2 are connected to the line wires 3 and4 through the coils comprising the windings 9 and 10 in series andwindings 11 and 12 in series respectively, which together form theretardation coil system 8. The condensers 13 and 14 and the coils 9, 10and 11, 12 in series therewith,provide a high impedance to the passageof voice frequency currents while each coil readily permits the passageof the telegraph signaling current to the sounders 1 and 2.

If there were any mutual coupling between the coil comprising thewindings 9 and 10 and the coil comprising windings 11 and 12 it canreadily be seen that one sounder would tend to be operated by thecurrent induced in the-coil connectedthereto when a signal is. beingtransmitted to the other sounder. Thus both sounders would respondwhen asignal is being transmitted over one of the lines, or it both lines werebeing used simultaneously, an unintelligent jumble of signals would bereceived atboth sounders.

At the same time it is evident that a signal common to but one sidev of,thel1ne would create a change in the inductanceot the coil associatedtherewith so that it is qulte es sentialthat means he provided forcausing. a s1m1lar change in'the other C011 or else the impedance ofboth sides of the line to voicelrequencies' would vary resulting inimproper operation of the phantom circuit. The retardation coil providesnegligible mutual coupling between the coils and'atthe same'timemaintains the inductance of both coils equal in the following manner.

Two cores 15 and 16,.identical in size and physical structure are eachwound with equal portions of each coil. The three windings 9, ,11, and12 are poled in the same direction while the winding 10 is poleddirection. 5

'Suppose now a; telegraph signal is being transmitted to the'sounder 1,the current will be such as to cause the flux inthe core 15; to be inthe direction of the arrow while the-same current will'cause the flux inthe othen core 16'to be in the-opposite direction by Virtue of thepolarity. of the winding 10.

The flux ineach core, will be of the same density, but'in'oppositedirections and the voltages induced in the windings 11' and 12 which aresimilarly wound will be opposite and balance each other. It can readilybe seen that a signal traversing the other coilcomprising windings 11and 12 will induce no voltage in its associated coil comprising windings9' and 10 for the same reason as setforth above. In this manner anytendency to cross-tirebetween the two soundersis eliminated. Tnorden'thatthere be no flux leakage from windings on one core to those onthe other, metallic shields 17 and18'areprovided' I It can further beseen that the magnetic path being wholly common to both coils, theinductance in both lines which may change due to'tel'egraph signals willnevertheless be the same inone coil as in'the other. ,In this manner.the tap 6 where the lead from the phantomcircuit joins the midpoint oftherepe-ating coil-secondary will always be at-the electrical center ofthe two lines.

' A similar retardation coil 8 is provided to drain the chargesaccumulated in the condensers-19 and 20 from the telegraph signals.

in the opposite Fig. 2 shows the manner in which the telephone linesaremaintained balanced where the telegraph circuits bridge the telephonerepeater. A two-way repeater for amplifying telephone signals is showncomprising the west to east repeater-WE, the east to west repeater EWand hybrid coils and 31 of well known type for separating the oppositelydirectedspeech 'signals..

A by-pass including the retardation. coil system 32 is provided aroundthe repeater for thetelegraph. signals which are excluded from therepeater circuit'bythe condensers 33, 38 34 and 34 and the retardationcoil systems 35 and 36, which furnish a. pathto ground for any of thetele raph charges which might collect on the aforementioned condensers.The retardation "coil system '32 in turn precludes any possibility ofthe voice signals being shunted around the re peater. The coil 32 is inall respects similar to that described in Fig 1 andprovides forbalancing both sidesof a telegraph; line regardless of the telegraphsigna ls, in either side of the line. i f Although this invention hasbeen de-. scribed in connection with s pecific embodi ments, it is to beunderstood that theinventhe appended claims.

What is claimed is: 7 4 p 1. in a transmission circuit, a line cir-"tion'is to be limited only by' the scope cuit, means for simultaneouslysuperposing voice signals and t'elegraph signals on said circuit, andmeans comprising a retardation coil system tor separating said signals,said retardation coil system comprising two coils having common fluxlinkage and portions, of their windings poled so as t oypracticallyeliminate mutual coupling between the coils.

2. In a transmission circuit, means for simultaneously superposingspeech signals and telegraph signals on said circuit, and means forseparating said signals, said means comprising a retardation coil systemhaving a plurality of cores with a plurality ioo of coils disposedthereon, one of said cores 7 having a portion of each "of said coilspiosed thereon, sa1d cores prov1d1ng common. 1

is: paths for said, coils, each of said coilsupon a pair or cores andhaving negligible,

prising a retardation coil system having two coils and two cores, halfof each of said coils being disposed on each of said cores, the windingsofone of said cores being in the Same direction, and the windings of theother of said cores being in opposite directions.

5. A combination in accordance with claim 4 in which the coils areenclosed in metallic shields.

6. In a signaling system adapted for the simultaneous transmission oftelephone and telegraph signals, the combination with a line circuit ofa terminal telephone circuit, and a plurality of telegraph circuits, acomposite set for directing the signals into their respective channels,said composite set comprising a retardation coil system having a coilassociated with each of said telegraph instruments, said coils havingflux paths wholly in common and poled so as to prevent mutual couplingtherebetween.

7 In a signaling system adapted for simultaneous transmission oftelephone and telegraph signals, the combination with a line circuit ofa terminal telephone circuit and a plurality of telegraph circuits, acomposite set for directing the signals into their respective channels,said composite set comprising two coils serially bridged across saidline circuit, each of said coils having windings disposed equally on apair of cores such that the flux paths of the coils are common, saidwindings being poled so that the voltage induced in the windings of onecoil due to a voltage impressed upon the other coil is negligible, saidcoils also being adapted so that a change in inductance of one coilresults in a corresponding change in inductance of the other.

8. In a transmission circuit, a line circuit,

means for simultaneously superposing voice signals and telegraph signalson said circuit, and means comprising a retardation coil system forseparating said signals, said system comprising a plurality of coilshaving common flux linkage and portions of their windings poled so as topractically eliminate mutual coupling between any of the coils.

In witness whereof, we hereunto subscribe our names this 17th day ofOctober A. D.,

ERNEST L. SCHWARTZ. ALBERT J. WILLIAMS, JR.

